Thank you for these clarifying texts! As a guitarist I always wondered about these things. However, I noticed that the discussion was mainly about Hauser and I wonder about my Armin Hanika FP60, which has a fairly thick soundboard (spruce) too. Some people have been amazed about the good projection is gives with such a thick soundboard. Is there a different rule of thumb for different kinds of wood? Does anybody know about the way Hanika thinks about this?

To answer the question....yes, you can use the 2.8mm soundboard and you can likely keep the strut dimensions the same...for typical spruce examples anyway. It's only .3 mm after all - The thickness of three sheets of copy paper....on a soundboard that would usually be considered overly thick at 2.8mm it isn't going to make any real difference.

I just fixed up a nice Spanish made Aria classical guitar for a local classical guitar student one of my friends teaches.. The owner dropped it off of her bicycle and the soundboard cracked in three spots, with a section of the top completely popped up above the surface. I measured the top thickness, and it was 3mm - solid cedar.
I fixed the guitar for her and strung it up with new strings and it was a decent sounding guitar. It had very little bracing in it - just three light fan braces.
So the moral of the story is how thick really depends on the bracing, the wood density, the sound your after etc. Personally, 3mm is too thick for a soundboard 90% of the time, but in this case it sounded OK. Not a great sounding guitar, but not bad either.
It really depends what you're after.

I just have a curious, or even "stupid" question to the luthiers: all discussions so far on soundboard thickness is obviously for solid tops, thus laminated top design(s) would be entirely different? And is there anything to say about typical thickness(es) of a laminated soundboard, especially at the sound hole?

What is the minimum thickness for soundboard? If a spruce soundboard has an average thickness of 28mm, can it still be used for a guitar top based on Segovia's Hauser 1937 that has a thickest part of about 31mm? Can we put taller or wider struts by say 2mm for all struts to increase strength? Would the sound be different?

After 1940s, Hauser used a thinner soundboard for a more Spanish methodology, as it was said. Anybody know the thickness range of Hauser guitars after 1940s?

Let's come at this another way: what is the 'correct' tempo for 'Leyenda'? Would you play it at the same speed in a large, reverberant room with a big audience as you would in a smaller 'dryer' space? What if you just had a cup of coffee, or maybe a glass of nice sherry? Hot day? I would hope that any performer would approach the matter of the tempo of a piece flexibly, depending on all of the wide range of factors that might bear on it. Why, then, would you insist that there is only one 'correct' thickness for a guitar top?

Let's come at this another way: what is the 'correct' tempo for 'Leyenda'? Would you play it at the same speed in a large, reverberant room with a big audience as you would in a smaller 'dryer' space? What if you just had a cup of coffee, or maybe a glass of nice sherry? Hot day? I would hope that any performer would approach the matter of the tempo of a piece flexibly, depending on all of the wide range of factors that might bear on it. Why, then, would you insist that there is only one 'correct' thickness for a guitar top?

Brune's comment is along these lines, noting that the 1937 Hauser Sr. with a "surprisingly thick top," . . . stands as a polar opposite to the exquisitely thin top of the 1912 Manuel Ramirez." He went on to state: "One has to wonder how important any of this is, if Segovia was thrilled with the sound of each instrument, and given the fact that neither seemed to last Segovia longer than about 25 years before being retired . . . [t]he logical conclusion would be that thicknesses are only part of the entire recipe of the guitar, and not a very important element at that." He closed with "[l]et your wood, experience, and intuition guide you, not your calipers." American Lutherie, #38, Summer 1994, p.25.

I'd add that this is one place where a bit of engineering can come in handy as well. You can measure the inherent stiffness of the wood, and calculate the 'proper' thickness based on that. Some experienced makers do this pretty reliably by flexing with their hands, but tests have shown that most people are not nearly as good at it as they think they are.

Let's come at this another way: what is the 'correct' tempo for 'Leyenda'? Would you play it at the same speed in a large, reverberant room with a big audience as you would in a smaller 'dryer' space? What if you just had a cup of coffee, or maybe a glass of nice sherry? Hot day? I would hope that any performer would approach the matter of the tempo of a piece flexibly, depending on all of the wide range of factors that might bear on it. Why, then, would you insist that there is only one 'correct' thickness for a guitar top?

Brune's comment is along these lines, noting that the 1937 Hauser Sr. with a "surprisingly thick top," . . . stands as a polar opposite to the exquisitely thin top of the 1912 Manuel Ramirez." He went on to state: "One has to wonder how important any of this is, if Segovia was thrilled with the sound of each instrument, and given the fact that neither seemed to last Segovia longer than about 25 years before being retired . . . [t]he logical conclusion would be that thicknesses are only part of the entire recipe of the guitar, and not a very important element at that." He closed with "[l]et your wood, experience, and intuition guide you, not your calipers." American Lutherie, #38, Summer 1994, p.25.

Bruné´s statement should not be misunderstood that the thickness of the top is of minor importance for the whole construction of a guitar.

The 1937 Hauser with its rather thick top definitely sounds different compared to the more fragile and thinner topped 1912 Manuel Ramirez.

I would describe the Hauser sound as more transparent and separating with well balanced and defined trebles, and rich harmonics, while the Manuel Ramirez has as a more fundamental very complex and dense sound, probably with a tendency more towards the bass, and less harmonics.

Having seen and handled both guitars in the Metropolitan Museum I can say that both instruments had highest quality spruce soundboards. The Hauser top would have done equally well much thinner in the Manuel Ramirez style and vice versa. I know later Hauser I guitars with comparable tops that are much thinner constructed, in some areas even below 2.0 mm, with a strutting pattern and strutting measurements like the 1937.

I would say that the thickness of a (very good) spruce top is highly important for the sound you try to achieve.

Well if the thickness of the soundboard is of no or little consequence then what part of a guitar is? We may as well all give up. GJO has this covered: it's what you are trying to achieve whilst taking into account the density/stiffness of the soundboard, the strutting also having some influence. Don't forget that Hauser I came from the N. European ladder braced/thicker soundboard tradition but obviously became increasingly influenced by the thinner soundboards of the Spanish model.

gjo wrote:
"The Hauser top would have done equally well much thinner in the Manuel Ramirez style and vice versa."

How do you know that?

If you measure a lot of softwood you'll find that the Young's modulus long the grain tracks the density pretty well. It's not perfect, of course; we're dealing with a natural material after all, but it's pretty reliable. The Young's modulus predicts how stiff a top will be at a given thickness, and can vary by more than a factor of two. Stiffness is what limits how thin we can make a top without running into trouble; if a top is stiff enough it will almost always be more than strong enough in normal use.

Young's modulus can be measured. Some experienced makers do this quite well with their hands. Most, it seems from some tests I've been told of, are not nearly as good as they think they are. Hauser and Manuel Ramirez may well have been better than most.

There is no reliable visual way to know the long grain Young's modulus of a top. It's not related to grain count, for example. Short of taking the top off the guitar, which I'm sure the museum would frown on, it would be hard to get a direct measurement of this. A CAT scan would give the density of the top directly, but I don't know if that's been done on that guitar. About 60% of the top wood samples I've measured have come within 10% of a given Young's modulus at a particular density, so you'd at least have some reasonable idea of what it might be with that information. Otherwise you're guessing, and I, for one, am loath to second guess Hauser or Ramirez.

Brune was very concerned about soundboard thickness. Years before the Hacklinger and then the MAG-ic Probe, Brune was measuring thickness with a digital device designed to measure paint thickness. Most of us were and many still are, flexing, prodding and tapping without such devices. Moreover, his plans provide a detailed account of the plate thicknesses. Most aspiring builders that I have come in contact with, want to know what thickness the plates should be. At first, one working alone or using the myriad of videos, books, etc. that exist today, is probably better off to work with a plan of one instrument, or at least, some reasonable fixed numbers until one gets experience with wood and the outcomes, and has some guitars that have been played and strung up for a while. Then, one can begin to heed Brune's observation, which I think was well-said. How thick should a top be? Well, Segovia was well satisfied with one guitar that had a very thick top, and then another with a rather thin top, so don't be constrained by a number. When working on the top, it is supremely important to use all the intelligence and experience one has to craft the best top one can. But that applies to each part of the guitar. As a system however, while the top may be significant in its contribution, each part is a contributor to the overall success or lack thereof of the guitar.

I asked:
"How do you know that?"
and gjo replied:
"Well, I would call it experience "

My point is, though, that you have no 'experience' with THAT top. Simply looking at it won't tell you what you really need to know; how stiff it will be along the grain at a given thickness. Hauser had that experience, and along with his notion of the sound he wanted to get, chose the thickness that he thought would work for that top. He was, apparently, right. Would he have been able to make a good guitar with that same top at less thickness? Probably, but it would not have been the same guitar, and may not have been nearly as successful. At this point there is no way to know.